Franklin Delano Roosevelt, commonly known by his initials FDR, holds the distinction of being the longest-serving President of the United States. His tenure extended from March 4, 1933, to April 12, 1945, spanning over twelve years in office. Roosevelt's presidency is notable not only for its duration but also for the significant impact it had on American society and the broader international landscape.

Born on January 30, 1882, in Hyde Park, New York, into a wealthy family, Roosevelt was a distant cousin of the 26th President, Theodore Roosevelt. He was educated at prestigious institutions, including Groton School, Harvard College, and Columbia Law School. Although he did not complete his law degree, he passed the bar examination and practiced law in New York City.

Roosevelt's political ascent began as a member of the New York State Senate, where he served from 1911 to 1913. His career continued to progress as he took on roles such as the Assistant Secretary of the Navy under President Woodrow Wilson and later, the Governor of New York from 1929 to 1932. His leadership during these various roles demonstrated his dedication to public service and his adherence to progressive ideas, which would later characterize his presidency.

Elected as the 32nd President of the United States during the Great Depression, Roosevelt implemented a series of programs and projects collectively known as the New Deal. These initiatives were designed to address the economic calamity through relief for the unemployed, recovery of the economy, and reform of the financial system. Landmark legislation during his first term included the Emergency Banking Act, the Civilian Conservation Corps, and the Social Security Act, which provided financial assistance to the elderly, the unemployed, and children.

Rooseverlt's influence extended beyond domestic policy. His leadership during World War II was critical in shifting the isolationist position that the U.S. had initially adopted towards a more active involvement. After the Japanese attack on Pearl Harbor on December 7, 1941, Roosevelt declared war on Japan and, subsequently, on Germany and Italy. His administration's support for the Allies was crucial before the U.S.'s full engagement in the war, exemplified by initiatives like the Lend-Lease program, which provided military aid to allied nations.

Re-elected for an unprecedented third term in 1940 and a fourth term in 1944, Roosevelt's health began to decline due to polio, which had earlier left him paralyzed from the waist down. Despite his illness, he remained dedicated to leading the nation through the war and planning for a peaceful post-war world. He was a key architect of the United Nations, envisioning an international body that would foster peace and cooperation to prevent future conflicts.

Roosevelt's presidency came to an end when he died on April 12, 1945, shortly before the end of World War II. His legacy, however, continues to influence the United States and the world. His leadership during one of the darkest times of the 20th century, his role in establishing key social safety nets, and his vision for international cooperation have cemented his status as a pivotal figure in American history.

Franklin D. Roosevelt's era marked significant transformations in U.S. domestic and foreign policies, and his tenure as the longest-serving president underscores the critical role he played at a time of profound national and global challenges. His strategies and policies not only guided the United States through depression and war but also reshaped the country's economic and political landscapes, leaving a lasting impact on subsequent generations.